Composite skull pins with reduced x-ray signature

ABSTRACT

A composite skull pin comprising:
         a core comprising a cone terminating in a distal point, the core being formed out of a substantially radiotranslucent material; and   a jacket comprising a hollow cone terminating in a sharp distal point, the hollow cone of the jacket being sized and shaped so that it overlies, and closely conforms to, the exterior of the cone of the core, the jacket being formed out of a strong, hard material, and further wherein the jacket has a sufficiently small mass such that the composite skull pin has a low X-ray signature.

REFERENCE TO PENDING PRIOR PATENT APPLICATION

This patent application claims benefit of pending prior U.S. ProvisionalPatent Application Ser. No. 61/069,104, filed Mar. 12, 2008 by EricBailey et al. for SKULL PINS WITH REDUCED X-RAY SIGNATURE (Attorney'sDocket No. NEUROLOGICA-24 PROV), which patent application is herebyincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to surgical procedures in general, and moreparticularly to intracranial surgical procedures.

BACKGROUND OF THE INVENTION

In many situations it may be necessary to perform an intracranialsurgical procedure. By way of example but not limitation, a patient mayhave suffered a large hemorrhagic stroke and may require accumulatedblood to be removed from the interior of the skull so as to relievepressure on the brain. Or the patient may have developed a tumor whichrequires removal. Or the patient may have suffered a cerebral injurywhich requires surgical intervention.

Regardless of the patient's underlying condition and the specificsurgical procedure which is to be performed, intracranial surgicalprocedures typically share a number of common aspects.

For one thing, due to the anatomy involved, intracranial surgicalprocedures generally require opening the skull at one or more locations,and then accessing specific sites within the interior of the skull inorder to effect a desired surgical procedure.

Furthermore, in view of the delicate neurological tissues present inthis region of the body, it is often necessary to stabilize thepatient's head with some sort of external framework during the surgicalprocedure. This external framework generally comprises amulti-dimensional frame which is positioned alongside different surfacesof the head, and a plurality of skull pins which extend from the frameinto engagement with the skull. By providing the skull pins with sharpdistal tips, and by configuring the frame so that the skull pins aredirected into the skull from a variety of different angles, the skullcan be stabilized during the surgical procedure. See, for example, FIG.1, which shows a head frame (formed out of stainless steel) offered byPro Med Instruments GmbH of Freiburg, Germany under the trade nameDORO™, and FIG. 2, which shows a skull pin (formed out of a stainlesssteel pin with a plastic mount) offered by Pro Med Instruments GmbHunder the trade name DORO™.

Additionally, since direct visualization is, at best, generally quitelimited within the intracranial spaces (e.g., due to the surroundingportions of the skull and, in many cases, the presence of interveningneurological tissues), it is frequently necessary (or, at the veryleast, highly desirable) to utilize scanners (e.g., X-ray devices, MRImachines, ultrasound imagers, etc.) before, during and after thesurgical procedure. Such scanners permit visualization of internaltissue structures even where direct visualization is not possible. Inthis respect it should be appreciated that the use of such scannersprior to, during and immediately following the surgical procedure can beextremely important in intracranial surgery, due to the restrictedfields of view, delicate neurological tissues and navigationrequirements. This is particularly true during the intracranialprocedure itself. In this respect it should also be appreciated thatX-ray devices (e.g., CT machines, C-arm fluoroscopes, etc.) aregenerally the most desirable type of scanner for use during intracranialsurgery, due to the high quality of their images, the ready availabilityof such devices within the operating suite, etc. MRI scanners aregenerally not preferred for intraoperative use for a variety of reasons,including the need to remove metal objects from the region of thescanner, etc.

Unfortunately, the need to use these X-ray devices during surgerycomplicates the design of the aforementioned head frame and skull pins.This is because forming the head frame and skull pins out of stainlesssteel (the traditional material of choice for operating room frames)dramatically undermines the quality of the X-ray image due to theenormous X-ray signature of stainless steel. See, for example, FIG. 3,which shows a typical X-ray image where no head frame and skull pins arepresent. Where the head frame and skull pins are formed out of stainlesssteel, large sections of the X-ray image (i.e., those sections which arealigned with the head frame and/or skull pins) are obscured and henceeffectively unusable.

In view of the foregoing, attempts have been made to fabricate the headframe and skull pins out of radiotranslucent materials. Thus, andlooking now at FIG. 4, there is shown another system offered by Pro MedInstruments GmbH of Freiburg, Germany under the trade name DORO™,wherein the head frame is made out carbon graphite (a material which issubstantially radiotranslucent) and only the skull pins are made out ofstainless steel. As can be seen in FIG. 5, this approach significantlyimproves the quality of the X-ray images. However, the presence of thestainless steel skull pins in the X-ray field still creates asignificant loss of image.

To this end, attempts have been made to fabricate the skull pins out ofradiotranslucent materials. Unfortunately, carbon graphite (the materialused to fabricate the radiotranslucent head frame) does not provide asatisfactory skull pin, since carbon graphite is too brittle to form thestrong, sharp distal tips needed to penetrate into the skull. Attemptsto use other radiotranslucent materials (e.g., various plastics) havealso proven to be unsatisfactory. As a result, skull pins are frequentlyformed out of metals (e.g., titanium) which have an X-ray signaturewhich is lower than the X-ray signature of stainless steel. Whileforming skull pins out of titanium generally results in X-ray imagessuperior to the images formed when using skull pins formed out ofstainless steel, there is still substantial image loss due to the X-raysignature of the titanium skull pins. See FIG. 6.

There is, therefore, a substantial need for a new approach for formingskull pins which have all of the strength and integrity needed toeffectively penetrate and grip the skull, yet which have a sufficientlysmall X-ray signature so as to permit the creation of X-ray images ofhigh quality.

SUMMARY OF THE INVENTION

The present invention provides a novel composite skull pin having all ofthe strength and structural integrity needed to effectively penetrateand grip the skull, yet which also provides a reduced X-ray signature soas to permit the creation of X-ray images of superior quality.

In one form of the invention, there is provided a composite skull pincomprising:

a core comprising a cone terminating in a distal point, the core beingformed out of a substantially radiotranslucent material; and

a jacket comprising a hollow cone terminating in a sharp distal point,the hollow cone of the jacket being sized and shaped so that itoverlies, and closely conforms to, the exterior of the cone of the core,the jacket being formed out of a strong, hard material, and furtherwherein the jacket has a sufficiently small mass such that the compositeskull pin has a low X-ray signature.

In another form of the invention, there is provided a method forscanning the head of a patient, comprising:

providing a head frame which is at least partially radiotranslucent, andproviding a composite skull pin, where the composite skull pincomprises:

-   -   a core comprising a cone terminating in a distal point, the core        being formed out of a substantially radiotranslucent material;        and    -   a jacket comprising a hollow cone terminating in a sharp distal        point, the hollow cone of the jacket being sized and shaped so        that it overlies, and closely conforms to, the exterior of the        cone of the core, the jacket being formed out of a strong, hard        material, and further wherein the jacket has a sufficiently        small mass such that the composite skull pin has a low X-ray        signature; and

securing the head of a patient to the head frame using the compositeskull pin.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore fully disclosed or rendered obvious by the following detaileddescription of the preferred embodiments of the invention, which is tobe considered together with the accompanying drawings wherein likenumbers refer to like parts, and further wherein:

FIG. 1 is a schematic view showing a prior art stainless steel headframe;

FIG. 2 is a schematic view showing a prior art skull pin comprising astainless steel pin with a plastic mount;

FIG. 3 is a schematic view showing a typical X-ray image where no headframe and skull pins are present;

FIG. 4 is a schematic view showing a prior art system comprising aradiotranslucent head frame and stainless steel skull pins;

FIG. 5 is a schematic view showing a typical X-ray image where the headframe is formed out of a radiotranslucent material and the skull pinsare formed out of stainless steel;

FIG. 6 is a schematic view showing a typical X-ray image where the headframe is formed out of a radiotranslucent material and the skull pinsare formed out of titanium;

FIG. 7 is an exploded schematic view showing a novel composite skull pinformed in accordance with the present invention;

FIG. 8 is a schematic side view showing the radiotranslucent carbongraphite core of the composite skull pin shown in FIG. 7;

FIG. 9 is a schematic distal end view of the radiotranslucent carbongraphite core shown in FIG. 8;

FIG. 10 is a schematic proximal end view of the radiotranslucent carbongraphite core shown in FIG. 8;

FIG. 11 is a schematic view showing the titanium jacket of the compositeskull pin shown in FIG. 7;

FIG. 12 is a schematic sectional view of the titanium jacket shown inFIG. 11;

FIG. 13 is a schematic view showing a typical X-ray image where the headframe is formed out of a radiotranslucent material and the skull pinsare formed with the composite construction shown in FIG. 7;

FIG. 14 is an exploded schematic view showing an alternative form ofcomposite skull pin formed in accordance with the present invention;

FIG. 15 is a schematic side view showing the composite skull pin shownin FIG. 14;

FIG. 16 is a schematic distal end view of the composite skull pin shownin FIG. 14;

FIG. 17 is a schematic proximal end view of the composite skull pinshown in FIG. 14; and

FIG. 18 is a schematic sectional view, taken along line 18-18 of FIG.17, showing the composite skull pin shown in FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Looking now at FIGS. 7-12, there is shown a novel composite skull pin 5formed in accordance with the present invention. Composite skull pin 5generally comprises a carbon graphite core 10 carrying, over a selectedportion of its exterior, a titanium jacket 15.

Carbon graphite core 10 makes up the primary mass of composite skull pin5 and is effectively radiotranslucent. In one preferred form of theinvention, carbon graphite core 10 comprises a cylindrical body 20having a cone 25 on its distal end and a cylinder 30 on its proximalend. Cone 25 terminates in a sharp tip 32 on its distal end. An annularshoulder 35 is formed at the intersection of cylindrical body 20 andcone 25, and an annular shoulder 40 is formed at the intersection ofcylindrical body 20 and cylinder 30. Annular shoulder 35 preferablyprovides a stop or support for the base 45 of titanium jacket 15, andannular shoulder 40 preferably provides a stop or support for mountingcomposite skull pin 5 in a head frame, as will be apparent to thoseskilled in the art in view of the present disclosure.

Titanium jacket 15 preferably covers only the distal tip of carbongraphite core 10. In one preferred form of the invention, titaniumjacket 15 comprises a hollow cone 50 for covering cone 25 of carbongraphite core 10. Hollow cone 50 terminates in a sharp tip 52 on itsdistal end. Hollow cone 50 is sized and shaped so that it can overlie,and closely conform to, the exterior of cone 25. Preferably, base 45 oftitanium jacket 15 engages annular shoulder 35 of carbon composite core10 when titanium jacket 15 is mounted on cone 25 of carbon graphite core10, so that the primary load of engaging the skull of the patient isborn by annular shoulder 35. Alternatively, hollow core 50 of titaniumjacket 15 and core 20 of carbon graphite core 10 may be formed so thatthe primary load of engaging the skull of the patient is distributedacross substantially the entire surface area of cone 20 of carbongraphite core 10.

Titanium jacket 15 provides the sharp distal tip of composite skull pin5 with the strength and integrity needed to penetrate the scalp and gripthe skull of a patient. However, titanium jacket 15 is preferably verythin, e.g., only about 0.010 inches thick or less, or some other minimalthickness, so that the titanium jacket constitutes very little mass andhence presents a minimal X-ray signature. See, for example, FIG. 13,which shows the X-ray image made using a composite skull pin formed inaccordance with the present invention, wherein the core of the compositeskull pin comprises carbon graphite and the distal tip jacket comprisestitanium. Note how the X-ray image of FIG. 13 is essentially devoid ofskull pin artifacts, due to the use of the composite skull pins of thepresent invention.

Titanium jacket 15 may be secured to carbon graphite core 10 using glueor epoxy, or the various parts may be machined or otherwise fabricatedso that no glue or epoxy is needed.

Thus, the novel skull pin of the present invention effectively comprisesa composite structure, utilizing two different components, formed out oftwo different materials, so as to provide a superior skull pin. Moreparticularly, the present invention provides a novel skull pincomprising (i) a core formed out of radiotranslucent carbon graphite,and (ii) a thin distal jacket formed out of strong, hard titanium. Thispermits the skull pin to have a low X-ray signature, since the majorportion of the skull pin (i.e., the core) is formed out ofradiotranslucent carbon graphite. At the same time, this constructionpermits the skull pin to have the strong, hard point needed to penetratethe scalp and grip the skull, since the distal tip of the core iscovered by a thin jacket of titanium. The titanium jacket isdeliberately made very thin (e.g., about 0.010 inches thick or someother minimal thickness) in order to constitute very little mass andhence present only a minimal X-ray signature.

See also FIGS. 14-18, which shows an alternative skull pin 5 alsoutilizing the novel composite construction of the present invention. Inthe composite skull pin 5 shown in FIGS. 14-18, cone 25 of carbongraphite core 10 is not mounted directly on cylindrical body 20 ofcarbon graphite core 10; rather, it is mounted to the distal end of acylinder 55 which is itself mounted to cylindrical body 20. Furthermore,titanium jacket 15 is not does not engage annular shoulder 35 of carbongraphite core 10; rather, the proximal end of titanium jacket 15comprises a plurality of fingers 60 which interlock with a plurality ofcounterpart fingers 65 formed on cylinder 55 so as to support titaniumjacket 15 about cone 25. As a result of this construction, the primaryload of engaging the skull of the patient is born by the interface offingers 60, 65, i.e. it is not born by the distal tip of carbon graphitecore 10.

If desired, the radiotranslucent core of the present invention can befabricated out of a suitable radiotranslucent material other than carbongraphite, and/or the strong, hard distal tip jacket of the presentinvention can be fabricated out of a material other than titanium, e.g.,a synthetic plastic material marketed by Integra LifeSciencesCorporation of Plainsboro, N.J. under the trade name Sapphire™.

Modifications of the Preferred Embodiments

It should be understood that many additional changes in the details,operation, steps and arrangements of elements, which have been hereindescribed and illustrated in order to explain the nature of the presentinvention, may be made by those skilled in the art while still remainingwithin the principles and scope of the invention.

What is claimed is:
 1. A composite skull pin comprising: a corecomprising a cone terminating in a distal point, the core being formedout of a substantially radiotranslucent material; and a jacketcomprising a hollow cone terminating in a sharp distal point, the hollowcone of the jacket being sized and shaped so that it overlies, andclosely conforms to, the exterior of the cone of the core, the jacketbeing formed out of a strong, hard material, and further wherein thejacket has a sufficiently small mass such that the composite skull pinhas a low X-ray signature.
 2. A composite skull pin according to claim 1wherein the core is formed out of carbon graphite.
 3. A composite skullpin according to claim 1 wherein the jacket is formed out of anon-radiotranslucent material.
 4. A composite skull pin according toclaim 1 wherein the jacket is formed out of titanium.
 5. A compositeskull pin according to claim 1 wherein the jacket is formed out of asynthetic plastic material of the type marketed by Integra LifeSciencesCorporation of Plainsboro, N.J. under the trade name Sapphire™.
 6. Acomposite skull pin according to claim 1 wherein the jacket has athickness of about 0.010 inches or less.
 7. A composite skull pinaccording to claim 1 wherein the core comprises a cylindrical bodyhaving the cone on its distal end and a cylinder on its proximal end,with a first annular shoulder being formed at the intersection ofcylindrical body and the cone, and a second annular shoulder beingformed at the intersection of cylindrical body and the cylinder.
 8. Acomposite skull pin according to claim 7 wherein the base of the jacketengages the first annular shoulder of the core.
 9. A composite skull pinaccording to claim 7 wherein the core comprises a cylindrical body,wherein the core is mounted to the core by a cylinder, and furtherwherein the base of the jacket engages portions of the cylinder.
 10. Amethod for scanning the head of a patient, comprising: providing a headframe which is at least partially radiotranslucent, and providing acomposite skull pin, where the composite skull pin comprises: a corecomprising a cone terminating in a distal point, the core being formedout of a substantially radiotranslucent material; and a jacketcomprising a hollow cone terminating in a sharp distal point, the hollowcone of the jacket being sized and shaped so that it overlies, andclosely conforms to, the exterior of the cone of the core, the jacketbeing formed out of a strong, hard material, and further wherein thejacket has a sufficiently small mass such that the composite skull pinhas a low X-ray signature; and securing the head of a patient to thehead frame using the composite skull pin.
 11. A method according toclaim 10 wherein the core is formed out of carbon graphite.
 12. A methodaccording to claim 10 wherein the jacket is formed out of anon-radiotranslucent material.
 13. A method according to claim 10wherein the jacket is formed out of titanium.
 14. A method according toclaim 10 wherein the jacket is formed out of a synthetic plasticmaterial of the type marketed by Integra LifeSciences Corporation ofPlainsboro, N.J. under the trade name Sapphire™.
 15. A method accordingto claim 10 wherein the jacket has a thickness of about 0.010 inches orless.
 16. A method according to claim 10 wherein the core comprises acylindrical body having the cone on its distal end and a cylinder on itsproximal end, with a first annular shoulder being formed at theintersection of cylindrical body and the cone, and a second annularshoulder being formed at the intersection of cylindrical body and thecylinder.
 17. A method according to claim 16 wherein the base of thejacket engages the first annular shoulder of the core.
 18. A methodaccording to claim 16 wherein the core comprises a cylindrical body,wherein the core is mounted to the core by a cylinder, and furtherwherein the base of the jacket engages portions of the cylinder.